“Gat Out Of Hell” is a stand-alone expansion to Saints Row IV, which I haven't played, but I did play “The Third” recently and was in the mood for more. “Gat Out Of Hell” doesn't have much story to it and you definitely can enjoy it without playing the other Saints Row games. However, I'd probably recommend playing one of them first just so you know who characters like Gat and Kenzie are.
Gat and Kenzie are the playable characters in this game, who go to hell in order to rescue the President after he gets taken to Hell during a Ouija board session. You need to get Satan's attention by causing havoc and taking control of Hell, which involves completing activities which were basically side-missions in the main games.
The core Saints Row gameplay is here, but it is set in Hell. The main difference is you can fly with demon wings. There's loads of orbs to collect which can upgrade your wings, your super dash, or abilities which are acquired throughout the game. One power is the ability to summon minions who attack nearby enemies.
Since you can fly, there's not much need to steal cars, but you can still do so. Many vehicles have their own challenge like to mow down people in the ambulance, or crush cars in the monster truck. Flying is really fun, and it becomes really fluid once you invest in a few upgrades to reduce your stamina depletion, and give you extra flaps to gain height. There's an ability that allows you to run up buildings as well which is definitely a cool ability.
There's certain aspects of the game that are removed: so there's a lack of customisation; no clothes/plastic surgery, you can't invest in properties, and there's no licensed music. The colour palette is a bit boring, since you have red sky, red lava, and lots of black.
There are a few missions which are basically the story missions. However, I don't think they are actually mandatory to reach the game's completion. There's a point in the game where all your acquaintances get captured. These acquaintances include Shakespeare, Blackbeard, Vladd the Impaler and the twins from Saints Row The Third. After this, I was meeting new people and they were instantly captured. It should be mandatory to meet everyone first since it made sense they would be captured all at once.
I felt that Satan appears a bit too early; I felt there was much more of the game to explore, although you do get to carry on playing after you have concluded the story.
Gat Out Of Hell is obviously a bit shallow, although it captures the essence of the Saints Row games. It may be short but it is very fun.